Sealing structure for an alkali battery having a gate on an aperture side of a sealing element

ABSTRACT

After a negative electrode current collector has been inserted into an insertion hole therein, a resin sealing element and negative electrode terminal plate are successively inserted into an aperture of a battery casing, and the aperture rim of battery casing is then bent inwards and crimped to seal aperture of battery casing. Sealing element is accommodated within battery casing in an arrangement facing negative electrode terminal plate, with resin injection gate corresponding to resin injection port of metal molds during resin molding thereof positioned at the aperture end of battery casing.

The present invention relates to an alkali battery, which employs astrongly alkaline liquid as electrolyte and of which aperture of thebattery casing is hermetically sealed by a sealing unit chieflyincluding resin.

BACKGROUND OF THE INVENTION

The typical construction of a cylindrical alkali battery, for example analkali dry battery is as shown in FIG. 5, which shows a longitudinalcross-section thereof. Specifically, within a battery casing (positiveelectrode) 1 of cylindrical shape having a head with a positiveelectrode terminal 8 projecting at its upper end face and an ornamentallabel 2 stuck on to its outer circumferential surface, there areinserted pellets of positive electrode mixture 3 which are molded incylindrical shape and consist of manganese dioxide and graphite added asconductive material. On the inside of this positive electrode mixture 3,there is poured in, separated by a separator 4, a gel-form zinc negativeelectrode 7 obtained by uniformly dispersing gelling agent and zincalloy powder in an alkaline electrolyte in which is dissolved potassiumhydroxide.

The aperture 1 a of battery causing 1 is sealed as follows. In aperture1 a at the bottom of battery casing 1, a rod-shaped negative electrodecurrent collector 10 made of brass is pressed into an insertion hole 9 aand a resin sealing element (gasket) 9 on to which is fitted aninsulating washer 11 made of metal is fitted thereon. Negative electrodecurrent collector 10 is then covered in electrically contacting fashionby a negative electrode terminal plate 12 contacting its head 10 a and afolded-back portion 9 b formed on resin sealing element 9 is stronglypressed against negative electrode terminal plate 12 by bending andcrimping inwards the edges of the bottom aperture of battery casing 1.

In the resin forming of sealing element 9, as shown in FIG. 6, a cavity18 constituting a molding space for sealing element 9 is formed by moldassembly of lower metal mold 13, upper metal mold 14 and mandrel metalmold 17, and molten resin 20 passing through a resin passage 19 a ofannular transverse cross-section of resin injection nozzle 19 is pouredinto this cavity 18 through a resin injection port 18 a formed inannular shape by upper metal mold 14, resin injection nozzle 19 andmandrel metal mold 17. When the resin 20 that has been injected hassolidified, the mold assembly constituted by lower metal mold 13, uppermetal mold 14 and mandrel metal mold 17 is broken open to obtain asealing element 9 as described above.

FIG. 7 shows a sealing unit 21 assembled using a resin sealing element 9formed by the molding steps described above. Sealing unit 21 isassembled by pressing in and inserting negative electrode currentcollector 10 from the open end on the opposite side to resin injectiongate 9 c corresponding to resin injection port 18 a when molding, intoinsertion hole 9 a in sealing element 9. Insulating washer 11 is thenmounted by bringing it into contact with inner seat 9 d and outer seat 9e, after which negative electrode terminal plate 12 is placed overinsulating washer 11, by bringing its central portion into contact withand mounting it on head 10 a of negative electrode current collector 10.In fitting this sealing unit 21 into aperture 1 a of battery casing 1,when bending the bottom aperture 1 a of battery casing 1 inwards, thefolded-back portion 9 b of resin sealing element 9 is strongly pushed onto negative electrode terminal plate 12 as shown by the arrow.

Due to their use of a strongly alkaline liquid which is an alkalineaqueous solution of high concentration and large ion conductivity evenat low temperature as electrolyte, such alkali batteries are able towithstand severe loading, have large capacity, and excellentlow-temperature characteristics, and as a result are employed inequipment where power such as in particular motor drive power is needed.On the other hand, the strongly alkaline liquid that is used aselectrolyte, due to its high permeability, is subject to the problemthat leakage tends to occur due to creeping. Accordingly, sealing ofaperture 1 a of battery casing 1 is performed by forcing negativeelectrode current collector 10 into the insertion hole 9 a, setting itsexternal diameter to a value larger than the hole diameter of insertionhole 9 a of resin sealing element 9, and bending and strongly crimpingthe aperture rim of battery casing 1.

However, in the case of the prior art sealing unit 21 shown in FIG. 7,small cracks appear in the resin injection gate 9 c when negativeelectrode current collector 10 is inserted into insertion hole 9 a ofsealing element 9 by forcing it in from one end aperture at the oppositeside to resin injection gate 9 c on molding, whilst piercing andbreaking flash 9 f of resin injection gate 9 c that closes the apertureat the other end, thereby widening this by pushing outwards. Since theresin injection gate 9 c where these cracks start is arranged in contactwith the electrolyte, electrolyte permeates into the cracks.

Also, in the case of high-temperature storage, heat cycle repetition, orprolonged storage at normal temperature, alkali batteries are subject toenvironmental stress cracking at locations subjected to excessive stressin a high-concentration alkaline aqueous solution (electrolyte)atmosphere. In particular, resin injection gate 9 c, due to the factthat resin deterioration tends to occur there because of the presence ofresidual stress on resin injection when molding, tends to constitute astarting point for the environmental stress cracks referred to abovewhich are generated and develop continuously. For example, where6,6-nylon is employed as the raw material of the sealing element 9, itis inferred that the high-concentration alkaline aqueous solution isselectively absorbed into non-crystalline portions that are present inthe crystalline layer, and cracks are created in the gaps betweennon-crystalline portions in the spherical crystals due to the jointaction of external stress and force of the absorbed alkaline aqueoussolution tending to wet and spread.

As a result, due to electrolyte that has permeated into the small cracksgenerated in the resin injection gate 9 c creeping up by the creepingphenomenon between the negative electrode current collector 10 and thehole circumferential surface of insertion hole 9 a of sealing element 9,cracks are continuously generated and developed originating from theresin injection gate 9 c which acquires residual stress during resinmolding. In this way, electrolyte permeates as the cracks develop andeventually leaks to the outside.

The present invention has been devised in view of the above problems,its object being to provide an alkali battery wherein the generation ofenvironmental stress cracks can be reliably prevented by a simpleconstruction and whereby excellent resistance to leakage can beobtained.

DISCLOSURE OF THE INVENTION

According to the present invention, in order to achieve the aboveobject, in an alkali battery wherein, after a negative electrode currentcollector has been inserted into an insertion hole therein, a resinsealing element and negative electrode terminal plate are successivelyinserted into an aperture of a battery casing, and the aperture rim ofsaid battery casing is then bent inwards and crimped to seal theaperture of said battery casing, said sealing element is accommodatedwithin said battery casing in an arrangement facing said negativeelectrode terminal plate, with a resin injection gate corresponding to aresin injection port of a metal mold during resin molding thereofpositioned at the aperture end of said battery casing.

With this alkali battery, since the resin injection gate correspondingto the resin injection port of the metal mold during resin molding ofthe sealing element is of a construction arranged at the aperture end ofthe battery casing and so not contacting the electrolyte, even if cracksare produced caused by residual stress during molding in the resininjection gate, electrolyte does not penetrate into these cracks, so thecracks do not develop to a sufficient degree to cause leakage ofelectrolyte. Excellent leakage-resistance performance can thereby beobtained.

Preferably in said invention the negative electrode current collector isforcibly inserted into an insertion hole passing through the centrallocation of the sealing element to extend into the interior of thebattery casing and is supported in a cantilevered manner, said insertionhole having a hole diameter smaller than the diameter of negativeelectrode current collector, and the sealing element has the resininjection gate at the aperture rim at the aperture end of said batterycasing in said insertion hole.

In this way, since the metal mold for resin molding of the sealingelement is of a construction in which a resin injection port is providedat the hole rim of the insertion hole in the middle of the cavity, resinmolding of the sealing element is easy. The negative electrode currentcollector is forced in from the aperture in the vicinity of the resininjection gate at the insertion hole of the sealing element, andalthough tiny cracks are produced in the resin injection gate which hasresidual stress on molding, these cracks are generated in a location onthe opposite side to the electrolyte in the sealing element, thus, incontrast to the conventional alkali battery, they do not constitute astarting point for the development of environmental stress cracks due topermeation of electrolyte. Apart from this, leakage due to penetrationof electrolyte by creeping between the sealing element and the negativeelectrode current collector can be reliably prevented since the negativeelectrode current collector is forced into an insertion hole of thesealing element whose hole diameter is set to be smaller than thediameter of the negative electrode current collector.

Also, according to the invention, the sealing element may be providedwith the resin injection gate in its face at the aperture edge side ofthe battery casing in a side part offset from its center.

As a result, since the resin injection gate is positioned in a side partof the sealing element remote from the insertion hole, there is nopossibility of cracks being produced therein when the negative electrodecurrent collector is forced into the insertion hole; consequently thenegative electrode current collector can be inserted by smoothly forcingit into the insertion hole.

Furthermore, a construction is desirable in which, in the invention, theaperture on the side adjacent the electrolyte in the insertion hole ofthe sealing element has a curved hole rim chamfered in radiused shape.Consequently, when the negative electrode current collector is insertedby forcing it into the insertion hole of the sealing element, there isno possibility of excessive stress being applied to the aperture rim ofthe insertion hole adjacent the electrolyte, so the generation ofenvironmental stress cracks at locations of the sealing element adjacentthe electrolyte can be reliably prevented; a further improvement inleakage resistance is thereby achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a molding step of a resinsealing element for an alkali battery according to an embodiment of thepresent invention;

FIG. 2 is a cross-sectional view showing a sealing unit of the abovealkali battery;

FIG. 3 is a cross-sectional view showing a molding step of a resinsealing element of an alkali battery according to another embodiment ofthe present invention;

FIG. 4 is a cross-sectional view showing a sealing unit of the abovealkali battery;

FIG. 5 is a longitudinal cross-sectional view showing the generalconstruction of an alkali battery according to the present invention;

FIG. 6 is a cross-sectional view showing the molding step of a prior artalkali battery sealing element; and

FIG. 7 is a cross-sectional view showing a sealing unit of the abovealkali battery.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention are described below indetail with reference to the drawings. FIG. 1 is a cross-sectional viewshowing the step of molding a resin sealing element used in an alkalibattery according to an embodiment of the present invention. In thisFigure, a lower metal mold 22, upper metal mold 23 and mandrel metalmold 24 are assembled, a cavity 27 constituting a molding space for thesealing element being formed within these. Molten resin 20 passingthrough resin passage 19 a, which is annular in cross-sectional shape,of resin injection nozzle 19 is injected through resin injection port 27a formed in annular shape by upper metal mold 23, resin injection nozzle19 and mandrel metal mold 24. After the injected resin 20 has hardened,the mold assembly constituted by lower metal mold 22, upper metal mold23 and mandrel metal mold 24 is broken open, to obtain a sealing element28 as shown in FIG. 2. In the molding of this sealing element 28, as isclear by comparison with FIG. 6 which shows a prior art molding step,the resin injection port 27 a of resin 20 injected by resin injectionnozzle 19 into cavity 27 is provided in a middle region of sealingelement 28 that is to be molded outside of the battery which does notcontact the electrolyte.

FIG. 2 shows a cross-sectional view of a sealing unit 29 constructedusing a sealing element 28 obtained by the molding step described above.In this Figure, sealing element 28 is provided with a resin casing 1 onthe side of aperture 1 a in insertion hole 28 a, and negative electrodecurrent collector 10 is inserted by being forced in as shown by thearrow from the one end aperture adjacent resin injection gate 28 c inthis insertion hole 28 a. After mounting on to sealing element 28 withinsulating washer 11 abutting inner seat 28 d and outer seat 28 e,negative electrode terminal plate 12 is mounted in a condition with itsmiddle part contacting head 10 a of negative electrode current collector10, overlying insulating washer 11, thereby constituting sealing unit29.

When sealing unit 29 assembled in this way is fitted into aperture 1 aof battery casing 1 as shown in FIG. 5, and the rim of the bottomaperture of battery casing 1 is then bent inwards and crimped, thefolded-back portion 28 b of resin sealing element 28 is strongly pressedon to negative electrode terminal plate 12 as shown by the arrow,thereby sealing aperture 1 a of battery casing 1 in liquid-tight manner.

When, in assembly of sealing unit 29, negative electrode currentcollector 10 is pressed into insertion hole 28 a of sealing element 28from one end aperture thereof corresponding to the resin injection gate28 c during molding, as a result of the insertion of negative electrodecurrent collector 10 into insertion hole 28 a whilst piercing andbreaking flash 28 f created during molding that closes one end aperturesuch as to push it outwards, tiny cracks are formed in resin injectiongate 28 c that retains residual stress from when it was molded. However,these cracks are generated in locations in sealing element 28 assembledin battery casing 1 which are on the opposite side to that of theelectrolyte. Consequently, with an alkali battery wherein aperture 1 aof battery casing 1 is closed in a sealed condition using the sealingunit 29 of FIG. 2, unlike the conventional alkali battery, the aforesaidcracks do not provide a starting point for environment stress cracksinduced by permeation of electrolyte. Furthermore, the resin injectiongate 28 c where cracks are liable to be produced because of the residualstress during molding is of a construction in which it is positioned onthe opposite side to the electrolyte in sealing element 28 and so doesnot contact the electrolyte. Even if cracks should be produced, suchcracks cannot develop to the extent of permitting leakage of electrolyteby permeation of electrolyte as happens in a conventional battery; thusthis battery has excellent leakage-resistance performance.

Furthermore, since the other-end aperture on the side that contacts theelectrolyte in the insertion hole 28 a of sealing element 28 isconstituted by a curved hole rim 28 g chamfered in radiused fashion,when negative electrode current collector 10 is inserted by forcing itinto insertion hole 28 a of sealing element 28, there is no possibilityof excess stress being applied to the other-end aperture of insertionhole 28 a that contacts the electrolyte. Leakage-resisting performancecan therefore be further raised since occurrence of environmental stresscracks at locations of the sealing element 28 contacting the electrolytecan be reliably prevented.

FIG. 3 is a cross-sectional view showing the process of molding a resinsealing element used in an alkali battery according to a furtherembodiment of the present invention. In this Figure, lower metal mold 22and mandrel metal mold 24 are the same as in the case of FIG. 1. Uppermetal mold 30, together with lower metal mold 22 and mandrel metal mold24, forms a cavity 27 of the same shape as in FIG. 1. However, incontrast to the cavity that is formed in annular shape in the middleposition in FIG. 1, the resin injection port 27 b of this cavity 27 inFIG. 3 is formed at a side location. Accompanying this, resin injectionnozzle 31, which is of ordinary configuration, fits into upper metalmold 30 and is arranged such that resin 20 can be injected into cavity27 through resin injection port 27 b from this resin injection nozzle31. It should be noted that resin injection ports 27 b of cavity 27could be formed at a plurality of side locations.

FIG. 4 shows a cross-sectional view of a sealing unit 33 constitutedusing a sealing element 32 obtained by the molding step described above.This sealing element 32 comprises an insertion hole 32 a of the sameshape as that of sealing element 28 of FIG. 2, a folded-back portion 32b, an inner seat 32 a, an outer seat 32 e and a curved hole rim 32 f.The sole difference from sealing element 28 of FIG. 2 lies in that aresin injection gate 32 c is provided on the inside face of the sidepart. Sealing unit 33 is constituted by mounting negative electrodecurrent collector 10, insulating washer 11 and negative electrodeterminal plate 12 on this sealing element 32 in the same way as in FIG.2.

With an alkali battery wherein aperture 1 a of battery casing 1 issealed in sealing condition using this sealing unit 33, when negativeelectrode current collector 10 is forced into insertion hole 32 a ofsealing element 32, resin injection gate 32 c is remote from insertionhole 32 a, so insertion by forcing in negative electrode currentcollector 10 can be effected in a smooth fashion without production ofcracks. Furthermore, since resin injection gate 32 c where cracks areliable to be generated due to the presence of residual stress duringmolding, as in the embodiment described above, is of a constructionpositioned at the face on the opposite side of sealing element 32 to theelectrolyte, so that it does not contact the electrolyte, just as in thecase of the alkali battery of the embodiment described above, excellentresistance to leakage can be obtained.

In order to ascertain the leakage-resistance performance of an alkalibattery according to the above embodiments, the following tests wereconducted. Resin sealing elements 28, 32 according to the embodimentswere respectively molded by the molding steps of FIG. 1 and FIG. 3,using 6,6-nylon as thermoplastic resin, and sealing units 29, 33 wereassembled respectively constituted as shown in FIG. 2 and FIG. 4 usingthese sealing elements 28, 32. Two types of alkali battery according tothe present invention were manufactured using these sealing units 29,33. As a comparative example, a conventional resin sealing element 9 wasmolded by the molding step of FIG. 6 likewise using 6,6-nylon and asealing unit 21 was assembled constituted as shown in FIG. 7 using thissealing element 9. An alkali battery constituting a comparison examplewas then manufactured using this sealing unit 21.

These alkali batteries were placed in a heat cycling atmosphere in whichthe temperature was varied with a heat cycle of 12 hours from 0° to 80°and their respective leakage-resistance performances were evaluated. Asa result, in the comparative example battery, axial cracks had developedto the extent of producing a defect by leakage of electrolyte, caused byentry of electrolyte into tiny cracks produced when the negativeelectrode current collector 10 in the resin injection gate 9 c wasformed in. In contrast, in the alkali batteries of the embodiments ofthe present invention, since the starting point for crack generation bypermeation of electrolyte was eliminated, defects due to leakage did notoccur. In the above test, it was found that leakage due to axial crackscould be effectively prevented if the ratio of the diameter of negativeelectrode current collector 10 with respect to the hole diameter ofinsertion hole 28 a of sealing element 28 was set in the range 101% to115%. It was also found that if this ratio was set to 100%, leakageoccurred due to creeping of electrolyte between the sealing element 28and negative electrode current collector 10.

It should be noted that the same benefits as described above could beobtained by employing, apart from the 6,6-nylon described above, vinylchloride, polypropylene, soft polyethylene, or polyethyleneterephthalate etc. as the material of sealing elements 28, 32.Furthermore, the same benefits as described above can be obtained bymolding sealing elements 28, 32 by any of the methods: cold runner,semi-hot runner and hot runner.

As set forth above, in the alkali battery according to the presentinvention, a construction is adopted wherein the resin injection gatecorresponding to the resin injection port of the metal mold during resinmolding of the sealing element is located at the aperture end of thebattery casing so that it does not contact the electrolyte. Even ifcracks are produced due to residual stress on molding in the resininjection gate, such cracks are not in contact with electrolyte, andtherefore they cannot develop to the extent of causing leakage ofelectrolyte; thus excellent leakage-resistance performance can beobtained.

What is claimed is:
 1. A method of producing an alkali batterycomprising the steps of: providing a battery casing having a first end,and a second end with an aperture; molding a sealing element having aninsertion hole extending from a first side, which is an outer side, to asecond side, which is an inner side, by injecting resin through aninjection gate on the first side; inserting a negative electrode currentcollector into the insertion hole of the sealing element; inserting thenegative electrode current collector and the sealing element in theaperture end of the battery casing; inserting a negative electrodeterminal plate in the aperture end of the battery casing adjacent thenegative electrode current collector; and bending a rim of the apertureof the battery casing, wherein the first side of the sealing element iscloser to the aperture of the battery casing than the second side of thesealing element and the second side of the sealing element is in contactwith an electrolyte.
 2. The method of producing an alkali batteryaccording to claim 1, wherein a diameter of the insertion hole of thesealing element is smaller than a diameter of the negative currentcollector, the negative electrode current collector is forcibly insertedinto the insertion hole of the sealing element to extend into thebattery casing and is supported in a cantilevered manner, and theinjection gate is provided at an aperture rim of the battery casing. 3.The method of producing an alkali battery according to claim 1, whereinthe injection gate is provided at a location offset from a centerlocation of the sealing element.
 4. A method of producing an alkalibattery comprising the steps of: providing a battery casing having afirst end, and a second end with an aperture; molding a sealing elementhaving an insertion hole extending from a first side, which is an outerside, to a second side, which is an inner side, by injecting resinthrough an injection gate on the first side; inserting a negativeelectrode current collector into the insertion hole of the sealingelement; inserting the negative electrode collector and the sealingelement in the aperture end of the battery casing; inserting a negativeelectrode terminal plate in the aperture end of the battery casingadjacent the negative electrode current collector; bending a rim of theaperture of the battery casing inwards and crimping the rim to seal theaperture of the battery casing; providing a negative electrode gel inthe battery casing; providing a positive electrode mixture in thebattery casing; providing a separator between the negative electrode geland the positive electrode mixture; and providing the insertion hole ofthe sealing element on a side contacting the negative electrode gelbeing constituted by a curved hole rim chamfered in radius shape,wherein the first side of the sealing element is closer to the apertureof the battery casing than the second side of the sealing element. 5.The method of producing an alkali battery according to claim 4, whereinthe second side of the sealing element is in contact with anelectrolyte.
 6. An alkali battery comprising: a battery casing having afirst end, and a second end with an aperture; a sealing element havingan insertion hole; said sealing element having a first side and a secondside; said sealing element being formed using an injection gate of thefirst side; a negative electrode current collector disposed in theinsertion hole of the sealing element; said negative electrode currentcollector and said sealing element disposed in the aperture end of thebattery casing; a negative electrode terminal plate disposed in theaperture end of the battery casing adjacent the negative electrodecurrent collector; and said aperture end of the battery casing beingbent inwards and crimped to seal the aperture of the battery casing,wherein the first side of the sealing element is closer to the apertureof the battery casing than the second side of the sealing element andthe second side of the sealing element is in contact with anelectrolyte.
 7. The alkali battery according to claim 6, wherein adiameter of the insertion hole of the sealing element is smaller than adiameter of the negative current collector, the negative electrodecurrent collector is forcibly inserted into the insertion hole of thesealing element to extend into the battery casing and is supported in acantilevered manner, and the injection gate is provided at an aperturerim of the battery casing.
 8. The alkali battery according to claim 6,wherein the injection gate is provided at a location offset from acenter location of the sealing element.
 9. An alkali battery comprising:a battery casing having a first end, and a second end with an aperture;a sealing element having an insertion hole; said sealing element havinga first side and a second side; said sealing element being formed usingan injection gate on the first side; a negative electrode currentcollector disposed in the insertion hole of the sealing element; saidnegative electrode current collector and said sealing element disposedin the aperture end of the battery casing; a negative electrode terminalplate disposed in the aperture end of the battery casing adjacent thenegative electrode current collector; said aperture end of the batterycasing being bent inwards and crimped to seal the aperture of thebattery casing; a negative electrode gel disposed in the battery casing;a positive electrode mixture disposed in the battery casing; a separatordisposed between the negative electrode gel and the positive electrodemixture; and the insertion hole of the sealing element on a sidecontacting the negative electrode gel being constituted by a curved holerim chamfered in radius shape, wherein the first side of the sealingelement is closer to the aperture of the battery casing than the secondside of the sealing element.
 10. The alkali battery according to claim9, wherein the second side of the sealing element is in contact with anelectrolyte.